Such linear motors have advantages in applications which require highly precise positioning, because by dispensing with an iron core in the primary part, disturbing cogging torques are avoided. However, in order to be able to bring about high forces, even without an iron core, the greatest possible coil currents are necessary, which may only be achieved with sufficient cooling of the coils.
U.S. Pat. No. 6,639,333 describes an ironless linear motor which drives the table of an exposure apparatus for manufacturing semiconductors. For precise positioning, it is important that the individual coils of the linear motor remain exactly at their intended position in the primary part, and do not shift relative to each other. This is ensured by a comb-like structure, in whose recesses flat coils are inserted. In order to cool the coils, they are jacketed by a housing in which a cooling medium is in direct contact with the coils.
The objectives of cooling and securing the coils are achieved in similar manner in U.S. Pat. No. 6,313,550, as well, in which structures for inserting the flat coils and a direct circumflow with a cooling medium are likewise described for an ironless planar motor.
Because of the great forces which act on the individual coils in the linear motor, and because of the possible problems with the insulation of the coils, given the direct circumflow with a cooling medium, it is advantageous if the coils are encapsulated with an electrically insulating, good heat-conducting synthetic resin that lends the coils additional stability, both against deformation and against shifting of the entire coil.
Thus, a linear motor is described in U.S. Pat. No. 5,723,917, in which the flat coils are encapsulated in a synthetic-resin block and disposed on a cooling plate that is used for the magnetic flux concentration, on one hand, and on the other hand, for cooling, by passing channels through it for a cooling medium. The synthetic-resin block is joined to the cooling plate with form-locking by noses on the cooling plate that project from the plate. However, the waste heat from the coils must always be dissipated to the cooling plate via an electrically insulating area, e.g., via the synthetic resin and/or further insulating layers. In addition, it is difficult to set the position of the coils exactly prior to the encapsulation with synthetic resin.